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Ionising radiation

Environmental Radioactivity - Medicine - Occupational Radiation Protection - Nuclear Hazards Defence

Ionisierende Strahlung

Polonium-210

  • Polonium-210 is the most common isotope of polonium in nature. It is formed as the last radioactive chain link in the radioactive decay chain of uranium-238. The total natural occurrence of polonium is extremely low.
  • Polonium-210 has a physical half-life of 138 days. It emits alpha particles during its radioactive decay to lead-206.
  • Radioactive polonium poses a health hazard only if the radionuclide is taken in by the body through food or drinking water, through breathing (inhalation) or if it enters the body through open wounds in the skin for example.
  • The amounts of polonium taken up naturally are so small that they virtually do not have any health effects. Hazardous health consequences can practically only occur due to accidental intake or the intentional (premeditated) administration of artificially produced polonium.

Glossary Entry Radionuclide

A radionuclide is an instable nuclide which decays into another nuclide spontaneously without extraneous cause emitting energy-rich (ionising) radiation. Currently more than 3,300 different nuclides are known which distribute over 118 currently known elements. Of these nuclides more than 3,000 nuclides are instable and radioactive.

Glossary Entry Incorporation

Generally: uptake into the body. Especially: uptake of radioactive substances into the human body.

Polonium is the chemical element with the atomic number 84. It is a silvery, radioactive metal that behaves similarly to tellurium and bismuth in chemical reactions. There are no stable isotopes of polonium. In nature, polonium-210 is the most common isotope of polonium. It is formed as the last radioactive chain link in the radioactive decay chain of uranium-238. The total natural occurrence of polonium is extremely low. On average, there is about 0.0002 microgram (µg) of polonium (corresponds to 2 x 10 to 10 ppm) in one tonne of soil.

Originally, polonium-210 was obtained by means of chemical separation from pitchblende or the decay products of radium. This, however, is very elaborate. Today polonium-210 can be produced more easily artificially by irradiating bismuth with neutrons in a nuclear reactor.

Uses

Polonium-210 is used

  • in combination with beryllium as a neutron source,
  • in anti-static electrodes/-brushes to eliminate static charges,
  • in highly sensitive optical and mechanical measuring instruments to eliminate static charges and
  • as a lightweight, thermoelectric generator in spaceflight.

Physical properties

Polonium-210 has a physical half-life of 138 days. It emits alpha particles during its radioactive decay to lead-206. The emitted alpha particles are highly energetic but they only have a very short range. In air, the range of an alpha particle is less than 4 centimetres, in human tissue (e.g. also in the skin) less than 0.1 millimetre.

Intake into the human body

Radioactive polonium poses a health hazard only if the radionuclide is taken up by the body (incorporation). This can occur

  • through intake with food or drinking water (ingestion)
  • through breathing (inhalation) or
  • through open wounds in the skin for example.

Owing to its natural occurrence, the annual average human intake via the pathways mentioned amounts to 58 Bq of polonium-210.

For smokers, the amount is increased by the natural polonium-210 content in tobacco taken up by the lungs. Intermediate products of the uranium-radium decay series can be deposited on tobacco leaves or taken up by the roots of the tobacco plant. Polonium-210 results from the radioactive decay of these intermediate products. A smoker who consumes 20 cigarettes per day adds an average of 29 Bq of polonium-210 to his annual intake.

Health effects

As polonium-210 emits very energetic alpha radiation, it has a high radiotoxicity; its chemical toxicity is orders of magnitude lower and is therefore not relevant for health assessment.

Following the intake of polonium through food or drinking water, a major part (50-90 %) is directly eliminated through the digestive tract. The remaining part is taken up by the blood in the gastrointestinal tract and is distributed - just like the polonium taken up by the lungs - throughout the body. In the process, the biological half-life of polonium-210 in the body is 50 days. That is to say: after 50 days, 50 % of the amount of the absorbed polonium is still in the body. The remainder is gradually eliminated in urine and faeces.

Basically, the health effects of polonium-210 depend on the amount taken up. The above-mentioned amounts of polonium taken up naturally are so small that they virtually do not have any health effects. An estimate shows that about 833 Bq of polonium-210 per year would have to be taken in through food (through ingestion) or 303 Bq of polonium per year would have to be taken up by the lungs (through inhalation) in order to reach a committed effective dose of about 1 milllisievert (mSv) per year.

Hazardous health consequences can practically only occur due to accidental intake or the intentional (premeditated) administration of artificially produced polonium. The mysterious death of former secret service officer Alexander Litvinenko on 23 November 2006 should be mentioned in this context. Very high polonium-210 activities were detected in his body. It is known from estimates that the uptake of about 20 MBq (20 million Bq) of polonium-210 can lead to death within a few days. As polonium-210 has a very high specific activity (1.67×1014 Bq/g), this activity - expressed in grams - corresponds to a very small amount (approx. 0.1 µg) of polonium-210.

Detection methods

Because polonium-210 only emits alpha radiation it cannot be detected by a whole body counter. For this reason, stool or urine samples need to be analysed in order to detect the incorporation of polonium. It is easier to detect the incorporation in urine samples than in stool samples. The limit of detection for polonium-210 in urine is so low that polonium in the body can already be detected far below the levels at which health effects are expected to occur.

State of 2017.03.20

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